The Tower of Pain / The Black City

The Black City is a ruined alien city in the frozen north that I'm building out as a campaign setting for eventual publication.  You can follow the project here.

The Decapitated Oracle

The Tower is area L on the City Map.  It's a lonely ruined spire north of the great glacier in the eastern part of the city ruins.  Whereas much of the Black City blends science fantasy and high adventure with Vikings, the Tower is one of the areas with a horror theme.

When the alien inhabitants of the city died in a mass extinction event, one of the last conscious acts involved turning on the Beacon, a massive radio signal to deep space requesting aid from other Greys.  No rescue ships came, but over the ages, various alien predators and space devils that lived in the void followed the signal back to earth, and some inhabit the ruins of the city even today.  One  group of these invaders is a colony of Mi-Go, alien scientists featured in the Lovecraft story, "The Whisperer in Darkness".

Early in the campaign, the characters might come into contact with rumors from other groups exploring the ruins, and hear how one of their sentries went missing, or other lone members of their expedition disappeared without a trace… as if they were lifted right up into the sky, leaving no tracks.  They've been taken by the Mi-Go.  The Mi-Go range outwards from the tower at night, looking for lone humans or Ape-Men to paralyze with their high tech implements and carry back to the tower.  (This is an ideal fate to inflict on a henchman, hired mercenary, or NPC friend of the players if they camp within 10 hexes of the tower).

Taken

If the characters somehow catch a glimpse of a silhouetted Mi-Go flying against the night sky, or discover the tower on their own, they'll find the tower is guarded by the headless bodies of Ape-Men, altered through Mi-Go surgery to have mouths in their abdomens along with body armor and bio weapons.  Alien symbiotes control the body's nervous systems and serve the Mi-Go.

Fighting their way up the tower to the higher levels, the characters might discover the Mi-Go "project" - an attempt to commune with an alien intelligence deep beneath the city through creation of the Decapitated Oracle.  The missing heads of the Mi-Go victims have been preserved and linked in a psychic circuit to allow the Mi-Go to contact the lingering thoughts and dreams of the dead city.  (In game terms, the Decapitated Oracle can be used to achieve a "Commune" effect for anyone with enough guts and mental toughness to put their hands on the control orb and try to use it… everyone else will be afflicted with Confusion as the various heads of the Oracle shout conflicting messages, prophecies and warnings all at the same time.)

The Mi-Go are one of the more insidious threats in the city, and the risk of a nightly abduction will become greater the more time the characters spend in the city, and the deeper into the ruins they push.  The players could experience some vicarious horror when an abduction happens to an NPC group first, building up the tension and fear of the unknown.  A disquieting sequence would involve one of their henchmen going missing, then battling the henchman's headless corpse sometime in the future if the characters discover the tower and come into contact with the Mi-Go servitors guarding it.  They'd learn the awful truth when the Oracle was finally discovered and the henchman's severed head spouts doom-filled prophecies at them.